Optical fiber bundle structure, optical connection structure, and method for manufacturing an optical fiber bundle structure

Abstract

To provide an optical fiber bundle structure that has a structure capable of improving a yield and a production throughput although having desired performance.SOLUTION: In a plurality of optical fibers 22, a second diameter part 32 has a larger diameter than a first diameter part 31. A tapered part 33 couples the first diameter part 31 and the second diameter part 32 to each other with a tapered surface. In a fiber housing part 40, a second housing part 43 has a larger inner diameter than a first housing part 41. Each first diameter part 31 is located at the first housing part 41. Each second diameter part 32 is located at the second housing part 43. The second housing part 43 includes a plurality of regions R1, R2 sectioned with a plurality of virtual planes orthogonal to a first direction. Tapered parts 33 of mutually adjacent optical fibers 22 among the plurality of optical fibers 22 are located in mutually different regions R1, R2, respectively.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present disclosure relates to an optical fiber bundle structure, an optical connection structure, and a method for manufacturing an optical fiber bundle structure.

Background Art

[0002] Patent Document 1 discloses an optical fiber bundle structure including a ferrule and a plurality of optical fibers accommodated in a fiber accommodating portion of the ferrule. Each of the plurality of optical fibers includes a first diameter portion and a second diameter portion having a diameter larger than that of the first diameter portion. The fiber accommodating portion includes a first accommodating portion and a second accommodating portion having an inner diameter larger than the inner diameter of the first accommodating portion. The first diameter portion of each optical fiber is accommodated in the first accommodating portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the optical fiber bundle structure disclosed in Patent Document 1, multiple optical fibers are housed in a first housing having an inner diameter smaller than the inner diameter of a second housing. In such a configuration, the optical fibers may be curved at the connection point between the first housing and the second housing. When optical fibers are curved, so-called bending loss can occur. In particular, in the first diameter housing where the diameter of the optical fiber is smaller than that of the second diameter housing, the diameter of the cladding is also smaller than that of the second diameter housing, making it easier for light to leak when the core is curved. Furthermore, in the above structure, during the manufacturing process, there is a risk that the optical fibers may break due to stress caused by the bending of the optical fibers within the fiber housing. If there is a structure that suppresses such bending loss and breakage in optical fibers, the yield and production throughput of products with the desired performance can be improved.

[0005] This disclosure aims to provide an optical fiber bundle structure and an optical connection structure having a structure that can improve yield and production throughput while having desired performance, as well as a method for manufacturing an optical fiber bundle structure that can suppress optical loss and breakage of optical fibers. [Means for solving the problem]

[0006] The optical fiber bundle structure according to this disclosure comprises a ferrule and a plurality of optical fibers. The ferrule includes a fiber housing. The fiber housing is formed in a hollow shape with a circular cross-section and extends in a first direction. The plurality of optical fibers are housed in the fiber housing. Each of the plurality of optical fibers includes a first diameter portion, a second diameter portion, and a tapered portion. The second diameter portion has a larger diameter than the diameter of the first diameter portion. The tapered portion connects the first diameter portion and the second diameter portion by a tapered surface. The tapered surface has a tapered shape. The fiber housing includes a first housing portion and a second housing portion. The second housing portion has an inner diameter larger than the inner diameter of the first housing portion. The first diameter portion of each of the plurality of optical fibers is located in the first housing portion. The second diameter portion of each of the plurality of optical fibers is located in the second housing portion. The second housing portion includes a plurality of regions divided by a plurality of virtual planes perpendicular to the first direction. Among multiple optical fibers, the tapered portions of adjacent optical fibers are located within different regions of each other.

[0007] The optical connection structure according to this disclosure comprises the optical fiber bundle structure and a multicore fiber. The multicore fiber includes a plurality of cores extending in a first direction and a cladding covering the plurality of cores. At least one of the plurality of cores included in the multicore fiber and at least one core of the plurality of optical fibers are optically coupled.

[0008] A method for manufacturing an optical fiber bundle structure according to this disclosure comprises the steps of preparing a ferrule and a plurality of optical fibers, pushing the plurality of optical fibers into the ferrule, and pulling the plurality of optical fibers. The ferrule includes a fiber housing portion. The fiber housing portion is formed in a hollow shape with a circular cross-section and extends in a first direction. The fiber housing portion includes a first housing portion and a second housing portion. The second housing portion has an inner diameter larger than the inner diameter of the first housing portion. The plurality of optical fibers are housed in the fiber housing portion. Each of the plurality of optical fibers includes a first diameter portion, a second diameter portion, and a tapered portion. The second diameter portion has a diameter larger than the diameter of the first diameter portion. The tapered portion connects the first diameter portion and the second diameter portion by a tapered surface exhibiting a tapered shape. In the step of pushing the plurality of optical fibers, the plurality of optical fibers are pushed into the ferrule so that the first diameter portions of the plurality of optical fibers are inserted into the first housing portion. In the step of pulling the plurality of optical fibers, after the plurality of optical fibers have been pushed into the ferrule, the plurality of optical fibers are pushed in the opposite direction to the direction in which they were pushed. The second housing section includes multiple regions divided by multiple virtual planes perpendicular to the first direction. In the process of pulling multiple optical fibers, the optical fibers are pulled in the opposite direction to the direction in which they were pushed in, while maintaining the state in which the first diameter portion of each optical fiber is located in the first housing section, the second diameter portion of each optical fiber is located in the second housing section, and the tapered portions of adjacent optical fibers are located in different regions among the multiple regions. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide an optical fiber bundle structure and an optical connection structure having a structure that can improve yield and production throughput while having desired performance, as well as a method for manufacturing an optical fiber bundle structure that can suppress optical loss and breakage of optical fibers. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a perspective view showing an optical connection structure in an embodiment. [Figure 2] Figure 2 is an exploded perspective view of the optical connection structure shown in Figure 1. [Figure 3] Figure 3 is a cross-sectional view of the optical connection structure shown in Figure 1 along line III-III. [Figure 4] Figure 4 shows the end face of the first optical fiber holder. [Figure 5] Figure 5 shows the end face of the second optical fiber holder. [Figure 6] Figure 6 is a magnified partial view showing a cross-section of the tip portion of the second optical fiber holder. [Figure 7] Figure 7 is a magnified view of the tip portion of an optical fiber. [Figure 8] Figure 8 is a partially enlarged view showing a cross-section of the tip portion of the ferrule in the first direction. [Figure 9] Figure 9 is a magnified view showing the tip portions of multiple optical fibers housed in the fiber housing. [Figure 10] Figure 10 is a graph showing the relationship between the bending of an optical fiber and the distance between tapered sections. [Figure 11] Figure 11 shows the end face of the second optical fiber holder in a modified example of the embodiment. [Figure 12] Figure 12 is a partially enlarged view showing a cross-section of the tip portion of the second optical fiber holder in a modified embodiment. [Modes for carrying out the invention]

[0011] [Description of Embodiments in this Disclosure] First, embodiments of this disclosure will be listed and described.

[0012] (1) The optical fiber bundle structure according to an embodiment of the present disclosure includes a ferrule and a plurality of optical fibers. The ferrule includes a fiber accommodating portion. The fiber accommodating portion is formed in a hollow shape with a circular cross-section and extends in a first direction. The plurality of optical fibers are accommodated in the fiber accommodating portion. Each of the plurality of optical fibers includes a first diameter portion, a second diameter portion, and a tapered portion. The second diameter portion has a diameter larger than the diameter of the first diameter portion. The tapered portion connects the first diameter portion and the second diameter portion by a tapered surface. The tapered surface exhibits a tapered shape. The fiber accommodating portion includes a first accommodating portion and a second accommodating portion. The second accommodating portion has an inner diameter larger than the inner diameter of the first accommodating portion. The first diameter portion of each of the plurality of optical fibers is located in the first accommodating portion. The second diameter portion of each of the plurality of optical fibers is located in the second accommodating portion. The second accommodating portion includes a plurality of regions divided by a plurality of virtual planes orthogonal to the first direction. The tapered portions of the adjacent optical fibers among the plurality of optical fibers are respectively located in different regions among the plurality of regions.

[0013] In the configuration of this optical fiber bundle structure, the tapered portions of the adjacent optical fibers among the plurality of optical fibers are respectively located in different regions among the plurality of regions. According to such a structure, the bending of the optical fiber is suppressed, and the bending loss and the breakage of the optical fiber are suppressed. Therefore, the bending loss in the optical fiber bundle structure is reduced, and the yield and the production throughput can be improved while having desired performance.

[0014] (2) In the optical fiber bundle structure of (1) above, the plurality of first diameter portions included in the plurality of optical fibers may be arranged at a first pitch in the first accommodating portion. The plurality of second diameter portions included in the plurality of optical fibers may be arranged at a second pitch greater than or equal to the first pitch in the second accommodating portion. In this case, the bending of the plurality of optical fibers can be further suppressed, and the bending loss and breakage of the plurality of optical fibers can be further suppressed.

[0015] (3) In the optical fiber bundle structure described in (1) or (2) above, the tapered portions of optical fibers that are not adjacent to each other may overlap when viewed from a direction perpendicular to the first direction. In this case, the size of the optical fiber bundle structure in the first direction can be reduced.

[0016] (4) In the optical fiber bundle structure of (1) or (2) above, the plurality of optical fibers may consist of four optical fibers. The tapered portions of the four optical fibers may each be located in different regions from each other among a plurality of regions. In this case, the bending of the optical fibers is further suppressed, and bending loss and breakage of the optical fibers are further suppressed.

[0017] (5) In any one of the optical fiber bundle structures described in (1) to (4) above, the length of the first housing portion in the first direction may be 2 mm or more. In this case, the gap between the first housing portion and the optical fiber is relatively small, so the effects of expansion and contraction of the resin portion are reduced. Therefore, with this configuration, the first diameter portion of each optical fiber is easily held in the first housing portion of the ferrule, and each optical fiber is less likely to shift relative to the ferrule.

[0018] (6) In any one of the optical fiber bundle structures described in (1) to (5) above, the distance between the tapered portions of adjacent optical fibers in the first direction may be 0.2 mm or more. In this case, the curvature of the optical fibers is further suppressed, and bending loss and optical fiber breakage are further suppressed.

[0019] (7) In any one of the optical fiber bundle structures described in (1) to (6) above, the tapered portions included in the multiple optical fibers may be housed within the second housing. In this case, the tapered portions of the multiple optical fibers can be protected by the ferrule. Therefore, the robustness of the optical fiber bundle structure can be improved.

[0020] (8) In any one of the optical fiber bundle structures described in (1) to (7) above, the distance between the tapered portions of adjacent optical fibers in the first direction may be 0.7 mm or less. In this case, the size of the optical fiber bundle structure in the first direction can be reduced.

[0021] (9) In the optical fiber bundle structures described in (1) to (8) above, adjacent optical fibers may be configured such that when light with a wavelength of 1.55 μm is passed through them in a state where they are wound once in a ring with a radius of curvature of 5 mm, the optical loss is 0.15 dB or less. In this case, bending loss in multiple optical fibers can be further suppressed.

[0022] (10) In the optical fiber bundle structures described in (1) to (9) above, adjacent optical fibers may be configured such that when light with a wavelength of 1.625 μm is passed through them in a state where they are wound once in a ring with a radius of curvature of 5 mm, the optical loss is 0.45 dB or less. In this case, bending loss in multiple optical fibers can be further suppressed.

[0023] (11) An optical connection structure according to another embodiment of the present disclosure comprises any one of the optical fiber bundle structures described in (1) to (10) above, and a multicore fiber. The multicore fiber includes a plurality of cores extending in a first direction and a cladding covering the plurality of cores. At least one of the plurality of cores included in the multicore fiber and at least one core of the plurality of optical fibers are optically coupled. With such a structure, bending of the optical fiber core is suppressed, and bending loss and optical fiber breakage can be suppressed. Thus, the optical connection structure can have reduced bending loss and improved yield and production throughput while having the desired performance.

[0024] (12) A method for manufacturing an optical fiber bundle structure according to yet another embodiment of the present disclosure comprises the steps of preparing a ferrule and a plurality of optical fibers, pushing the plurality of optical fibers into the ferrule, and pulling the plurality of optical fibers. The ferrule includes a fiber housing portion. The fiber housing portion is formed in a hollow shape with a circular cross-section and extends in a first direction. The fiber housing portion includes a first housing portion and a second housing portion. The second housing portion has an inner diameter larger than the inner diameter of the first housing portion. The plurality of optical fibers are housed in the fiber housing portion. Each of the plurality of optical fibers includes a first diameter portion, a second diameter portion, and a tapered portion. The second diameter portion has a diameter larger than the diameter of the first diameter portion. The tapered portion connects the first diameter portion and the second diameter portion by a tapered surface exhibiting a tapered shape. In the step of pushing the plurality of optical fibers, the plurality of optical fibers are pushed into the ferrule such that the first diameter portions of the plurality of optical fibers are inserted into the first housing portion. In the process of drawing multiple optical fibers, after the multiple optical fibers are pushed into the ferrule, the multiple optical fibers are pushed in the opposite direction to the direction in which they were pushed. The second housing contains multiple regions divided by multiple virtual planes perpendicular to the first direction. In the process of drawing multiple optical fibers, while maintaining the state in which the first diameter portion of each of the multiple optical fibers is located in the first housing, the multiple optical fibers are pulled in the opposite direction to the direction in which they were pushed, such that the second diameter portion of each of the multiple optical fibers is located in the second housing, and the tapered portions of adjacent optical fibers are located in different regions among the multiple regions. In this case, an optical fiber bundle structure with suppressed bending of the optical fibers can be manufactured. As a result, bending loss and optical fiber breakage can be suppressed. [Details of the embodiments of this disclosure]

[0025] Specific examples of embodiments of this disclosure will be described below with reference to the drawings. The present invention is not limited to these examples, and is intended to include all modifications within the meaning and scope of the claims, as defined by the claims. In the description of the drawings, identical elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0026] Figure 1 is a perspective view showing an optical connection structure according to one embodiment. Figure 2 is an exploded perspective view of the optical connection structure shown in Figure 1. Figure 3 is a cross-sectional view of the optical connection structure shown in Figure 1 along line III-III. As shown in Figures 1 to 3, the optical connection structure 1 comprises a first optical fiber holder 10, a second optical fiber holder 20, and a split sleeve S. The first optical fiber holder 10 has a multicore fiber 12 (hereinafter also referred to as "MCF12"), a ferrule 14, and a flange 16. The second optical fiber holder 20 has a plurality of optical fibers 22, a ferrule 24, a resin part 25, and a flange 26. The second optical fiber holder 20 has an optical fiber bundle structure. The split sleeve S is a member that holds and aligns the ferrules 14 and 24 from the outside so that the optical axes of each core of the MCF12 of the first optical fiber holder 10 are aligned with the optical axes of each core of the plurality of optical fibers 22.

[0027] The MCF12 extends in direction A, which corresponds to the longitudinal direction of the MCF12. As shown in Figures 3 and 4, the MCF12 has a plurality of cores 12a extending in direction A, a cladding 12b extending in direction A and covering the plurality of cores 12a together, and a tip surface 12c. Figure 4 shows the end face of the first optical fiber holder 10. Figure 4 shows the tip of the MCF12 and the end face of the ferrule 14. The tip surface 12c is composed of the tips of the plurality of cores 12a and the tip of the cladding 12b. The cores 12a may be made of silica glass to which a dopant such as germanium has been added to increase the refractive index, and the cladding 12b may be made of silica glass to which a dopant such as fluorine has been added to lower the refractive index, and the combination of materials and dopants can be appropriately selected. In such an MCF12, an optical signal of a predetermined wavelength can be propagated by each core 12a.

[0028] In MCF12, for example, each core 12a is arranged in a two-dimensional manner. As shown in Figure 4, MCF12 has, for example, four cores 12a in a single fiber. The number of cores 12a in MCF12 is not limited to this. In the example shown in Figure 4, four cores 12a are arranged in a square. The mode field diameter of each core 12a may be, for example, 15 μm or less, or 5 μm or more. The core pitch of each core 12a may be, for example, 20 μm or more and 80 μm or less. "Core pitch" corresponds to the distance between the centers of the cores in a cross section perpendicular to direction A. The diameter of the cladding 12b may be, for example, 200 μm or less, 125 μm or less, 100 μm or less, 80 μm or less, or 50 μm or more.

[0029] The ferrule 14 is a cylindrical member that holds the tip portion 12d of the MCF 12, and has an inner hole 14a which is a through hole that accommodates the tip portion 12d of the MCF 12, and an end face 14b of the ferrule 14. The ferrule 14 fixes the tip portion 12d of the MCF 12 to the inner hole 14a such that the tip face 12c of the MCF 12 is exposed inside the end face 14b. The inner diameter of the inner hole 14a is the same as or slightly larger than the outer diameter of the MCF 12, and the tip portion 12d of the MCF 12 is fitted by being inserted into the inner hole 14a. The length of the ferrule 14 in direction A is, for example, 6 mm or more and 11 mm or less. The ferrule 14 is made of a ceramic material such as zirconia or a glass material.

[0030] As shown in Figure 3, the flange 16 is a cylindrical member that holds the rear end portion of the ferrule 14 and houses the MCF 12 inside. The portion of the MCF 12 housed within the flange 16 may be fixed inside the flange 16 with an adhesive or the like. The flange 16 is made of, for example, metal or resin.

[0031] The multiple optical fibers 22 are optical fibers that are optically connected to the MCF 12. Each optical fiber 22 has a core 22a extending in direction A, a cladding 22b extending in direction A and covering the core 22a, and a tip surface 22c, as shown in Figures 3 and 5. Figure 5 is a diagram showing the end surface of the second optical fiber holder 20. Figure 5 shows the tips of the multiple optical fibers 22 and the end surface of the ferrule 24. The tip surface 22c is composed of the tip of the core 22a and the tip of the cladding 22b. The core 22a may be made of silica glass to which a dopant such as germanium has been added to increase the refractive index, and the cladding 22b may be made of silica glass to which a dopant such as fluorine has been added to lower the refractive index, and the combination of materials and dopants can be appropriately selected. In such optical fibers 22, an optical signal of a predetermined wavelength is propagated by each core 22a. Each of the multiple optical fibers 22 is a single-core optical fiber having one core. As a variation of this embodiment, each of the multiple optical fibers 22 may be, for example, an optical fiber bundle structure including a multicore optical fiber, or a structure in which single-core optical fibers and multicore optical fibers are mixed.

[0032] In the second optical fiber holder 20, each optical fiber 22 is arranged in a two-dimensional manner when viewed from direction A. As shown in Figure 5, the second optical fiber holder 20 has, for example, four optical fibers 22. Each optical fiber 22 is, for example, a single-mode optical fiber. Each optical fiber 22 has a unimodal refractive index distribution profile. In a modified example of this embodiment, each optical fiber 22 may have a layer between the core 22a and the cladding 22b with a refractive index lower than that of the cladding 22b, and may have a trench-type refractive index distribution profile. In another modified example of this embodiment, each optical fiber 22 may be a multimode optical fiber.

[0033] The number and arrangement of cores 22a of the optical fibers 22 in the second optical fiber holder 20 correspond to the number and arrangement of multiple cores 12a of the MCF 12 in the first optical fiber holder 10. In other words, the arrangement of each core 22a of the multiple optical fibers 22 matches the arrangement of multiple cores 12a of the MCF 12. However, the total number and arrangement of cores 22a of the multiple optical fibers 22 do not need to perfectly match the number and arrangement of cores 12a of the MCF 12, and some may not be optically connected. The cores 22a of the multiple optical fibers 22 in the second optical fiber holder 20 are configured to optically couple with each core 12a of the MCF 12 in the first optical fiber holder 10 by rotational adjustment around the central axis of the ferrule 24.

[0034] In the optical connection structure 1, at least one of the multiple cores 12a contained in the MCF 12 is optically coupled to at least one core 22a of the multiple optical fibers 22. For example, if the optical fiber 22 is a single-mode single-core optical fiber, there is a one-to-one correspondence between each core 22a of the optical fiber 22 and the core 12a of the MCF 12 of the first optical fiber holder 10. For example, if the optical fiber 22 is a multi-core optical fiber, there is a correspondence between the multiple cores 22a in one optical fiber 22 and the multiple cores 12a of the MCF 12 of the first optical fiber holder 10.

[0035] Each optical fiber 22 is configured such that, for example, when wound in a ring shape with a radius of curvature of 5 mm, the optical loss when light with a wavelength of 1.550 μm is transmitted through it is 0.15 dB or less. Each optical fiber 22 is configured such that when wound in a ring shape with a radius of curvature of 5 mm, the optical loss when light with a wavelength of 1.625 μm is transmitted through it is 0.45 dB or less. Each optical fiber 22 may have both the above characteristics for light with a wavelength of 1.550 μm and the above characteristics for light with a wavelength of 1.625 μm, or it may have only one of the characteristics.

[0036] The ferrule 24 is a cylindrical member that holds together the tip portions 22d of multiple optical fibers 22, and has an inner bore 24a, which is a through-hole that accommodates each tip portion 22d of the multiple optical fibers 22, and an end face 24b. The ferrule 24 is made of, for example, a ceramic material such as zirconia or a glass material.

[0037] The ferrule 24 fixes the tip portions 22d of the multiple optical fibers 22 within the inner hole 24a by the resin portion 25 such that the respective tip faces 22c of the multiple optical fibers 22 are exposed inside the end face 24b of the ferrule 24. The inner diameter of the inner hole 24a is the same as or slightly larger than the outer diameter of the bundle of multiple optical fibers 22, and the tip portions 22d of the multiple optical fibers 22 are inserted into the inner hole 24a and bonded and fixed by the resin portion 25 that fills the gaps between them.

[0038] The resin part 25 is, for example, a wire-binding adhesive. The resin part 25 is, for example, a thermosetting adhesive, which can be cured by heating after being injected into a predetermined location. When the ferrule 24 is mainly made of ceramic material, the resin part 25 is, for example, a thermosetting epoxy adhesive or a thermosetting acrylic adhesive. When the ferrule 24 is mainly made of glass material, the resin part 25 is, for example, a thermosetting epoxy adhesive, a thermosetting acrylic adhesive, an ultraviolet-curing epoxy adhesive, or an ultraviolet-curing acrylic adhesive. The resin part 25 is not limited to, but depends on, the material of the ferrule 24.

[0039] As shown in Figure 3, the flange 26 is a cylindrical member that holds the rear end portion of the ferrule 24 and houses multiple optical fibers 22 inside. In other words, the flange 26 corresponds to the holding portion that holds the ferrule 24. The portions of the multiple optical fibers 22 housed within the flange 26 may be fixed inside the flange 26 with adhesive or the like. The flange 26 is made of, for example, metal or resin.

[0040] Next, an example of the second optical fiber holder 20 in this embodiment will be described in more detail with reference to Figures 6 to 9. Figure 6 shows a cross-section of the tip portion of the second optical fiber holder 20 in direction A. Figure 7 shows the tip portion of the optical fiber 22. Figure 8 shows a cross-section of the tip portion of the ferrule 24 in direction A. Figure 9 is a partially enlarged view showing the tip portions of multiple optical fibers housed in the fiber housing.

[0041] The ferrule 24 includes a fiber housing section 40. The fiber housing section 40 is filled with a resin section 25. The fiber housing section 40 is formed in a hollow shape with a circular cross-section and extends in direction A. The fiber housing section 40 corresponds to the inner hole 24a described above. Multiple optical fibers 22 are housed in the fiber housing section 40.

[0042] As shown in Figures 6 and 7, each of the multiple optical fibers 22 includes a first diameter portion 31, a second diameter portion 32, and a tapered portion 33. The first diameter portion 31 corresponds to the small diameter optical fiber portion and is smaller than the general outer diameter. The first diameter portion 31 is formed by a small diameter processing using, for example, etching with hydrofluoric acid solution. The second diameter portion 32 corresponds to the portion with the general outer diameter. In other words, the second diameter portion 32 has a larger diameter than the diameter of the first diameter portion 31. The tapered portion 33 includes a tapered surface 33a. The tapered surface 33a has a tapered shape. The tapered portion 33 connects the first diameter portion 31 and the second diameter portion 32 by the tapered surface 33a. The outer diameter of the optical fiber 22 gradually decreases from the second diameter portion 32 toward the first diameter portion 31.

[0043] The diameter of the first diameter portion 31 is, for example, 20 μm or more and 80 μm or less. In the configuration shown in Figure 7, the diameter of the first diameter portion 31 is 40 μm. The diameter of the second diameter portion 32 is, for example, 50 μm or more and 200 μm or less. In the configuration shown in Figure 7, the diameter of the second diameter portion 32 is 125 μm.

[0044] Each optical fiber 22 further includes a covering portion 34. The covering portion 34 covers the outer shape of the optical fiber 22 in a portion having a diameter similar to that of the second diameter portion 32. The covering portion 34 has a larger diameter than the diameter of the second diameter portion 32. The diameter of the covering portion 34 is, for example, 170 μm or more and 260 μm or less. In the configuration shown in Figure 7, the diameter of the covering portion 34 is 250 μm.

[0045] As shown in Figure 5, at the tip surface 22c, the diameter of the circumscribed circle of the first diameter portion 31 corresponds to the cladding diameter of the MCF 12. The diameter of the circumscribed circle of the first diameter portion 31 corresponds to the inner diameter of the inner bore 24a of the ferrule 24. At the tip surface 22c, multiple optical fibers 22 are packed tightly in the inner bore 24a in a two-dimensional manner. "Two-dimensional tight packing" means that the maximum number of optical fibers 22 that can be placed in the inner bore 24a are arranged so that each optical fiber 22 does not move within the inner bore 24a. For example, at the inner bore 24a of the tip surface 22c, multiple optical fibers 22 are arranged so that they are in contact with each other. A clearance (gap) may be provided between the multiple optical fibers 22 and the inner bore 24a. At the tip surface 22c, if the diameter of each of the four first diameter portions 31 is 40 μm and the inner diameter of the inner bore 24a is 96.6 μm, then the clearance between the multiple optical fibers 22 and the inner bore 24a is zero.

[0046] The mode field diameter of each core 22a is, for example, 15 μm or less. The mode field diameter of each core 22a may be, for example, 5 μm or more. At the tip surface 22c, the core pitch of each core 22a is, for example, 20 μm or more and 80 μm or less. At the tip surface 22c, the diameter of the cladding 22b is, for example, 20 μm or more and 125 μm or less. The inner diameter of the inner bore 24a of the ferrule 24 is, for example, 200 μm or less. The diameter of the circumscribed circle may be, for example, 125 μm or less, 100 μm or less, 80 μm or less, or 50 μm or more.

[0047] As shown in Figures 6 and 8, the fiber housing section 40 includes a first housing section 41, an inner diameter conversion section 42, and a second housing section 43. In Figure 6, the two dashed lines shown on each optical fiber 22 indicate the boundary B1 between the first diameter section 31 and the tapered section 33, and the boundary B2 between the second diameter section 32 and the tapered section 33, respectively. The two dashed lines shown on the ferrule 24 indicate the boundary B3 between the first housing section 41 and the inner diameter conversion section 42, and the boundary B4 between the inner diameter conversion section 42 and the second housing section 43, respectively.

[0048] The second housing section 43 has an inner diameter larger than the inner diameter of the first housing section 41. The inner diameter conversion section 42 has a tapered shape. The inner diameter conversion section 42 connects the first housing section 41 and the second housing section 43 by a tapered surface. The inner diameter conversion section 42 may also connect the first housing section 41 and the second housing section 43 by a curved surface.

[0049] The first diameter portion 31 of each of the multiple optical fibers 22 is located in the first housing portion 41, the inner diameter conversion portion 42, and the second housing portion 43. The second diameter portion 32 of each of the multiple optical fibers 22 is not located in the first housing portion 41 or the inner diameter conversion portion 42, but is located only in the second housing portion 43. The entirety of the multiple tapered portions 33 contained in the multiple optical fibers 22 is located within the second housing portion 43. Each optical fiber 22 is spaced apart from the inner surface 44a of the ferrule 24 in the inner diameter conversion portion 42. The inner surface 44a is the surface that defines the inner hole 24a.

[0050] The ferrule 24 in direction A has, for example, a length of 6 mm or more and 11 mm or less in direction A. The ferrule 24 is made of a ceramic material such as zirconia or a glass material. In the configuration shown in Figure 8, the length of the ferrule 24 in direction A is 6.5 mm. The length of the first housing portion 41 in direction A, i.e., the extending direction of the ferrule 24, is, for example, 2 mm or more. The length of the inner diameter conversion portion 42 in the extending direction of the ferrule 24 is, for example, 1 mm or more. The length of the second housing portion 43 in the extending direction of the ferrule 24 is, for example, 2 mm or more. The connection portion between the first diameter portion 31 and the second diameter portion 32 of each optical fiber 22 is at least 0.5 mm away from the boundary B4 between the inner diameter conversion portion 42 and the second housing portion 43 in direction A. The boundary B1 between the first diameter portion 31 and the tapered portion 33 of each optical fiber 22 is at least 0.5 mm away from the boundary B4 between the inner diameter conversion portion 42 and the second housing portion 43 in direction A.

[0051] The multiple first diameter portions 31 contained in the multiple optical fibers 22 are arranged in a first pitch in the first housing portion 41 of the fiber housing portion 40, when viewed from direction A. The first pitch is, for example, the core pitch of the core 22a in the first diameter portion 31. The multiple second diameter portions 32 contained in the multiple optical fibers 22 are arranged in a second pitch or higher in the second housing portion 43 of the fiber housing portion 40, when viewed from direction A. The second pitch is, for example, the core pitch of the core 22a in the second diameter portion 32.

[0052] When the first diameter portions 31 of adjacent optical fibers 22 are in contact, the first pitch is equal to the sum of the radius of the first diameter portion 31 of one of the adjacent optical fibers 22 and the radius of the first diameter portion 31 of the other. In other words, when the first diameter portions 31 of adjacent optical fibers 22 are in contact, the first pitch is the sum of the outer diameters of the first diameter portions 31 of the adjacent optical fibers 22 divided by 2. Therefore, if the outer diameters of the first diameter portions 31 of adjacent optical fibers 22 are equal, the first pitch is equal to the outer diameter of the first diameter portion 31. When the first diameter portions 31 of adjacent optical fibers 22 are not in contact, the first pitch is greater than the sum of the outer diameters of the adjacent optical fibers 22 divided by 2. Similarly, when the second diameter portions 32 of adjacent optical fibers 22 are in contact, the second pitch is equal to the sum of the radius of the second diameter portion 32 of one of the adjacent optical fibers 22 and the radius of the second diameter portion 32 of the other. In other words, when the second diameter portions 32 of adjacent optical fibers 22 are in contact, the second pitch is the sum of the outer diameters of the second diameter portions 32 of the adjacent optical fibers 22 divided by 2. Therefore, if the outer diameters of the second diameter portions 32 of adjacent optical fibers 22 are equal, the second pitch is equal to the outer diameter of the second diameter portion 32. If the second diameter portions 32 of adjacent optical fibers 22 are not in contact, the second pitch is greater than the outer diameter of the second diameter portion 32.

[0053] When a clearance is provided between multiple optical fibers 22 and the inner bore 24a, the pitch in which the optical fibers 22 are arranged can vary within the range of the clearance. The clearance between the first diameter portion 31 of multiple optical fibers 22 and the inner bore 24a of the first housing portion 41 is smaller than the clearance between the second diameter portion 32 of multiple optical fibers 22 and the inner bore 24a of the second housing portion 43. The clearance between the first diameter portion 31 of multiple optical fibers 22 and the inner bore 24a of the first housing portion 41 is substantially zero. For example, if the diameter of each of the four first diameter portions 31 at the tip surface 22c is 40 μm, the inner diameter of the inner bore 24a of the first housing portion 41 is configured to be approximately 97 μm. If the diameter of each of the four second diameter portions 32 is 125 μm, the inner diameter of the inner bore 24a of the second housing portion 43 is configured to be approximately 310 μm or more and 400 μm or less.

[0054] Due to the clearance between the second diameter portions 32 of the multiple optical fibers 22 and the inner bore 24a of the second housing portion 43, the second diameter portions 32 may be positioned randomly within the second housing portion 43. For this reason, at least one pair of second diameter portions 32 of the multiple optical fibers 22 are arranged in the fiber housing portion 40 at a pitch greater than or equal to the outer diameter of the second diameter portion 32 when viewed from direction A. The pitch at which the second diameter portions 32 of the first group of multiple optical fibers 22 are arranged may be greater than the pitch at which the second diameter portions 32 of the second group of multiple optical fibers 22 are arranged. The first group and the second group are groups consisting of multiple second diameter portions 32 with different combinations. The same second diameter portion 32 may be included in the first group and the second group. For example, adjacent second diameter portions 32 in the first group may be touching each other, while adjacent second diameter portions 32 in the second group may be spaced apart from each other.

[0055] As shown in Figure 9, the tapered portions 33 of adjacent optical fibers 22 are offset from each other in direction A. In other words, the tapered portions 33 of adjacent optical fibers 22 do not overlap when viewed from a direction perpendicular to direction A.

[0056] In the configuration shown in Figures 5 and 6, all tapered portions 33 of the multiple optical fibers 22 do not overlap when viewed from a direction perpendicular to direction A. In a modified example of this embodiment, the tapered portions 33 of optical fibers 22 that are not adjacent to each other may overlap when viewed from a direction perpendicular to direction A.

[0057] As shown in Figure 9, the second housing section 43 includes multiple regions R1 and R2, which are divided by multiple virtual planes perpendicular to direction A. These multiple virtual planes include, for example, a virtual plane containing the boundary B1 of the optical fiber 22 and a virtual plane containing the boundary B2 of the optical fiber 22. The tapered portions 33 of adjacent optical fibers 22A and 22B are each located within different regions R1 and R2. For example, the tapered portion 33 of optical fiber 22A is located within region R2. For example, the tapered portion 33 of optical fiber 22B is located within region R1. For example, region R1 is the region sandwiched between the boundary B1 and the boundary B2 of optical fiber 22B. For example, region R2 is the region sandwiched between the boundary B1 and the boundary B2 of optical fiber 22A.

[0058] For example, if the multiple optical fibers 22 housed in the fiber housing section 40 consist of four optical fibers 22, the tapered portions 33 of the four optical fibers 22 are each located in different regions among the multiple regions mentioned above.

[0059] Referring to Figures 9 and 10, the relationship between the distance L between the tapered portions 33 of adjacent optical fibers 22 and the curvature of the optical fibers 22 will be explained. Figure 9 is a partially enlarged view showing the tip portions of multiple optical fibers 22 housed in the fiber housing 40.

[0060] For example, as shown in Figure 9, multiple optical fibers 22 include adjacent optical fibers 22A and 22B. For example, the tapered portion 33 of optical fiber 22B is closer to the first housing portion 41 of the fiber housing portion 40 than the tapered portion 33 of optical fiber 22A. The curvature of adjacent optical fibers 22A depends on the distance L between the tapered portions 33 of adjacent optical fibers 22A and 22B in direction A. Hereinafter, the distance between the tapered portions 33 of optical fibers 22A and 22B in direction A will also be called the "inter-tapered portion distance".

[0061] For example, the curvature of the first diameter portion 31 of adjacent optical fibers 22A depends on the distance in direction A between the boundary B1 between the first diameter portion 31 and the tapered portion 33 of optical fiber 22A and the contact point C1 between the first diameter portion 31 of optical fiber 22A and optical fiber 22B. The contact point C1 corresponds, for example, to the contact point between the first diameter portion 31 of optical fiber 22A and the boundary B2 between the second diameter portion 32 and the tapered portion 33 of optical fiber 22B.

[0062] In optical fiber 22A, the bending radius of the first diameter portion 31 between boundary B1 and contact point C1 is "R", and the angle between the normal passing through contact point C1 and the extension of boundary B1 is "θ1". "Bending radius" corresponds to "radius of curvature". In direction A, the line segment S1 between boundary B2 of optical fiber 22B and boundary B1 of optical fiber 22A corresponds to the distance L between the tapered portions of optical fibers 22A and 22B in direction A. The line segment S2 between the intersection point of the central axis CE and the extension of boundary B2 of optical fiber 22B and the intersection point of the central axis CE and boundary B1 of optical fiber 22A can be expressed as S2 = Rθ1. In this case, the distance L between the tapered portions of optical fibers 22A and 22B in direction A is expressed by the following equation (1).

number

[0063] If the diameter of the first diameter portion 31 is "d1" and the diameter of the second diameter portion 32 is "d2", then equation (2): Rθ1sin(θ2)=d3=(d2-d1) / 2 is satisfied. θ2 corresponds to θ1 / 2. If θ1 / 2 is sufficiently small, then the following equation (3) is satisfied.

number

[0064] Equation (4) is derived from equations (2) and (3).

number

[0065] Equation (5) is derived by transforming equation (4).

number

[0066] Equation (6) is derived from equations (2) and (5).

number

[0067] Equation (7) is derived by transforming equation (6).

number

[0068] Figure 10 is a graph showing the relationship between the bending radius R of optical fiber 22A and the distance L between tapered sections. For example, the diameter d1 of the first diameter section 31 is 0.04 mm, and the diameter d2 of the second diameter section 32 is 0.125 mm. When the distance L between the tapered sections of adjacent optical fibers 22A and 22B is 0.3 mm, the bending radius R is 0.7 mm. When the distance L between the tapered sections of adjacent optical fibers 22A and 22B is 0.35 mm, the bending radius R is 1.0 mm. When the distance L between the tapered sections of adjacent optical fibers 22A and 22B is 0.6 mm, the bending radius R is 3 mm. When the distance L between the tapered sections of adjacent optical fibers 22A and 22B is 0.83 mm, the bending radius R is 5.7 mm. The longer the distance L between the tapered sections of adjacent optical fibers 22A and 22B, the larger the bending radius R. Therefore, the larger the distance L between the tapered portions of adjacent optical fibers 22A and 22B, the smaller the bending of the optical fibers 22A and 22B. In other words, the larger the distance L between the tapered portions, the more the bending of the optical fibers 22A and 22B can be suppressed. If the distance L between the tapered portions of adjacent optical fibers 22A and 22B is 0.35 mm, a bending radius R of at least 1 mm can be ensured.

[0069] If the distance L between the tapered portions of adjacent optical fibers 22A and 22B is too large, the tapered portion 33 or the first diameter portion 31 of the optical fiber 22 may protrude from the rear end of the ferrule 14. In this case, since the strength of the tapered portion 33 and the first diameter portion 31 is relatively weak, the robustness will be reduced.

[0070] For example, consider the case where four optical fibers 22 are housed in the fiber housing 40, and all of the tapered portions 33 of the four optical fibers 22 are arranged so that they do not overlap when viewed from a direction perpendicular to direction A. For example, if the length of the second housing 43 in the ferrule 14 is 2.5 mm, it is preferable that the distance L between the tapered portions is 0.83 mm or less.

[0071] In direction A, the distance L between the tapered portions of adjacent optical fibers 22A and 22B is 0.7 mm or less. In direction A, the distance L between the tapered portions of adjacent optical fibers 22A and 22B is 0.2 mm or more. In other words, the tapered portions 33 of adjacent optical fibers 22 are separated by 0.2 mm or more in direction A.

[0072] The second optical fiber holder 20 described above is manufactured, for example, by the following process. First, a ferrule 24 and multiple optical fibers 22 are prepared.

[0073] Next, the multiple optical fibers 22 are pushed into the ferrule 24 so that the first diameter portions 31 of each optical fiber 22 are inserted into the first housing portion 41 of the ferrule 24. The direction of pushing is along direction A. At this time, the first diameter portion 31 of each optical fiber 22 is inserted into the first housing portion 41, and each optical fiber 22 is exposed from the end face 24b of the ferrule 24. In this state, for example, the tapered portion 33 of at least one optical fiber 22 is located in the inner diameter conversion portion 42 of the ferrule 24.

[0074] Next, after the multiple optical fibers 22 are pushed into the ferrule 24, the multiple optical fibers 22 are pulled in the opposite direction to the direction in which they were pushed, while maintaining the state in which the first diameter portion 31 of each of the multiple optical fibers 22 is located in the first housing portion 41. At this time, the multiple optical fibers 22 are pulled in the opposite direction to the direction in which they were pushed, such that the second diameter portion 32 of each of the multiple optical fibers 22 is located in the second housing portion 43, and the tapered portions 33 of adjacent optical fibers 22 are located in different regions R1 and R2 within the second housing portion 43. Regions R1 and R2 are regions divided by multiple virtual planes perpendicular to direction A.

[0075] By pulling multiple optical fibers 22, the bending of the multiple optical fibers 22 is eliminated. By pulling multiple optical fibers 22, the first diameter portion 31 of each optical fiber 22 is located in the first housing portion 41, the inner diameter conversion portion 42, and the second housing portion 43, and each optical fiber 22 is separated from the inner surface 44a of the ferrule 24 in the inner diameter conversion portion 42. For example, the multiple optical fibers 22 are pulled such that the connection portion between the first diameter portion 31 and the tapered portion 33 of each optical fiber 22 is at least 0.5 mm away from the boundary between the inner diameter conversion portion 42 and the second housing portion 43 in direction A.

[0076] Next, the resin portion 25 is filled into the fiber housing portion 40 and solidified. As a result, each optical fiber 22 is fixed to the ferrule 24. The second optical fiber holder 20 is manufactured through the above process.

[0077] Next, the optical fiber bundle structure in a modified example of this embodiment will be described with reference to Figures 11 and 12. Figure 11 is a diagram showing the end face of the second optical fiber holder. Figure 12 is a partially enlarged view showing a cross-section of the tip portion of the second optical fiber holder. This modified example is generally similar to or the same as the embodiment described above. In this modified example, the second optical fiber holder 20 differs from the embodiment described above in that it has seven optical fibers 22. The differences between the embodiment described above and this modified example will be mainly described below.

[0078] In this modified example, as shown in Figure 11, the second optical fiber holder 20 has seven optical fibers 22. In this case, the MCF 12 has seven cores 12a. In Figure 12, the two dashed lines shown on each optical fiber 22 indicate the boundary B1 between the first diameter portion 31 and the tapered portion 33, and the boundary B2 between the second diameter portion 32 and the tapered portion 33, respectively. The two dashed lines shown on the ferrule 24 indicate the boundary B3 between the first housing portion 41 and the inner diameter conversion portion 42, and the boundary B4 between the inner diameter conversion portion 42 and the second housing portion 43, respectively.

[0079] At the tip surface 22c, the diameter of the circumscribed circle of the first diameter portion 31 corresponds to the cladding diameter of the MCF 12. The diameter of the circumscribed circle of the first diameter portion 31 corresponds to the inner diameter of the inner bore 24a of the ferrule 24. At the tip surface 22c, seven optical fibers 22 are closely packed in the inner bore 24a in a two-dimensional manner.

[0080] In the configurations shown in Figures 11 and 12, the tapered portions 33 of optical fibers 22 that are not adjacent to each other may overlap when viewed from a direction perpendicular to direction A. In the configurations shown in Figures 11 and 12, the tapered portions 33 of optical fibers 22 that are adjacent to each other are offset from each other in direction A. In other words, the tapered portions 33 of optical fibers 22 that are adjacent to each other do not overlap when viewed from a direction perpendicular to direction A.

[0081] The tapered portions 33 of adjacent optical fibers 22 are each located in different regions among a plurality of regions. For example, among the seven tapered portions 33 of optical fibers 22, adjacent optical fibers 22 are each located in different regions among the plurality of regions. The tapered portions 33 of optical fibers 22 that are not adjacent among the seven optical fibers may overlap when viewed from a direction perpendicular to direction A.

[0082] Next, with reference to Figures 10 and 11, the effects of the optical fiber bundle structure of the optical connection structure 1 and the second optical fiber holder 20 will be explained.

[0083] In the configuration of the second optical fiber holder 20, the tapered portions 33 of adjacent optical fibers 22A and 22B are located in different regions R1 and R2 from a plurality of optical fibers 22. With this structure, bending of the optical fiber 22 is suppressed, and bending loss and breakage of the optical fiber 22 are suppressed. Therefore, bending loss in the second optical fiber holder 20 is reduced, and yield and production throughput can be improved while maintaining the desired performance. When the positions of the tapered portions 33 of the plurality of optical fibers 22 overlap in direction A, that is, when the tapered portions 33 of the plurality of optical fibers 22 are located in the same region, the bending of the first diameter portion 31 is relatively large.

[0084] In the second optical fiber holder 20, adjacent optical fibers 22A and 22B may be configured such that when light with a wavelength of 1.55 μm is passed through them while they are wound in a ring shape with a radius of curvature of 5 mm, the optical loss is 0.15 dB or less. In this case, the bending loss in multiple optical fibers 22A and 22B can be further suppressed.

[0085] In the second optical fiber holder 20, adjacent optical fibers 22A and 22B may be configured such that, when wound in a ring shape with a radius of curvature of 5 mm, the optical loss when light with a wavelength of 1.625 μm is transmitted through them is 0.45 dB or less. In this case, the bending loss in multiple optical fibers 22 can be further suppressed.

[0086] In the second optical fiber holder 20, the length of the first housing portion 41 in direction A may be 2 mm or more. In this case, the gap between the first housing portion 41 and the optical fiber 22 is relatively small, so the effects of expansion and contraction of the resin portion 25 are reduced. Therefore, with this configuration, the first diameter portion 31 of each optical fiber 22 is easily held in the first housing portion 41 of the ferrule 24, and each optical fiber 22 is less likely to shift relative to the ferrule 24. Furthermore, the longer the first housing portion 41, the more the positional accuracy of the tip surface 22c of each optical fiber 22 relative to the ferrule 24 can be improved.

[0087] In the second optical fiber holder 20, the multiple first diameter portions 31 may be arranged in the first housing portion 41 at a first pitch. The multiple second diameter portions 32 may be arranged in the second housing portion 43 at a second pitch greater than or equal to the first pitch. In this case, the bending of the multiple optical fibers 22 can be further suppressed, and the bending loss and breakage of the multiple optical fibers 22 can be further suppressed.

[0088] In the second optical fiber holder 20, the plurality of optical fibers 22 may consist of four optical fibers 22. The tapered portions of the four optical fibers 22 may each be located in different regions from a plurality of regions. In this case, the bending of the optical fibers 22 is further suppressed, and bending loss and breakage of the optical fibers 22 are further suppressed.

[0089] In the second optical fiber holder 20, the tapered portions 33 of optical fibers 22A and 22B that are not adjacent to each other may overlap when viewed from a direction perpendicular to direction A. In this case, the size of the second optical fiber holder 20 in direction A can be reduced.

[0090] In the second optical fiber holder 20, the distance between the tapered portions 33 of adjacent optical fibers 22 in direction A may be 0.2 mm or more. In this case, the curvature of the optical fiber 22 is further suppressed, and bending loss and breakage of the optical fiber 22 are further suppressed.

[0091] In the second optical fiber holder 20, the multiple tapered portions 33 included in the multiple optical fibers 22 may be housed within the second housing portion 43. In this case, the tapered portions 33 of the multiple optical fibers 22 can be protected by the ferrule 24. Therefore, the robustness of the optical fiber bundle structure can be improved.

[0092] In the second optical fiber holder 20, the distance L between the tapered portions of adjacent optical fibers 22 in the first direction may be 0.7 mm or less. In this case, the size of the second optical fiber holder 20 in direction A can be reduced.

[0093] In the second optical fiber holder 20, the first diameter portion 31 is reduced in diameter, and its strength is weak. In particular, stress tends to concentrate at the connection point between the reduced diameter first diameter portion 31 and the non-reduced second diameter portion 32 when the optical fiber 22 is bent. This connection point may break due to the concentrated stress. Also, because the cladding of the reduced diameter first diameter portion 31 is thin, if the first diameter portion 31 is bent, light seeping out from the core 22a is easily lost. For example, if the clearance between multiple optical fibers 22 and the inner hole 24a is relatively small, friction occurs when the first diameter portions 31 of multiple optical fibers 22 are inserted into the first housing portion 41. Therefore, as shown in Figures 10 and 11, the first diameter portion 31 of multiple optical fibers 22 may bend when they are pushed into the first housing portion 41.

[0094] In the second optical fiber holder 20, the first diameter portion 31 is located in the first housing portion 41, the inner diameter conversion portion 42, and the second housing portion 43. Each optical fiber 22 is spaced apart from the inner surface 44a of the ferrule 24 in the inner diameter conversion portion 42. With this structure, the bending of the core 22a of the optical fiber 22 is suppressed, and bending loss and breakage of the optical fiber 22 are suppressed. Therefore, bending loss in the second optical fiber holder 20 is reduced, and yield and production throughput can be improved while maintaining the desired performance.

[0095] The shorter the length of the first housing portion 41, the lower the adhesive force between the first diameter portions 31 of the multiple optical fibers 22 and the inner surface 44a of the first housing portion 41 by the resin portion 25. The resin portion 25 expands or contracts in response to changes in ambient temperature or humidity. Therefore, the expansion and contraction of the resin portion 25 may cause the position of the optical fibers 22 relative to the ferrule 24 to shift.

[0096] In the second optical fiber holder 20, the pitch at which the second diameter portions 32 of the first group of multiple optical fibers 22 are arranged is greater than the pitch at which the second diameter portions 32 of the second group of multiple optical fibers 22 are arranged. With this configuration, the bending of the multiple optical fibers 22 can be further suppressed, and the bending loss and breakage of the multiple optical fibers can be further suppressed.

[0097] Although embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above embodiments and can be applied to various embodiments. For example, Figure 5 shows a configuration in which the second optical fiber holder 20 has four optical fibers 22, and Figure 11 shows a configuration in which the second optical fiber holder 20 has seven optical fibers 22. However, the number of optical fibers 22 in the second optical fiber holder 20 is not limited thereto. For example, the second optical fiber holder 20 may have three optical fibers 22, eight optical fibers 22, or nineteen optical fibers 22. Similarly, the MCF 12 may have three cores 12a, eight cores 12a, or nineteen cores 12a. [Explanation of symbols]

[0098] 1… Optical connection structure 10…First optical fiber holder 12…MCF 12a... Core 12b...Clad 12c…Tip surface 12d...Tip part 14…Ferrule 14a...Inner hole 14b...end face 16…Flange 20…Second optical fiber holder 22… Fiber optic 22a... Core 22b...Clad 22c…Tip surface 22d…Tip part 22A… Optical fiber 22B… Optical fiber 24... Ferrule 24a…Inner hole 24b...end face 25… Resin part 26…Flange 31...First diameter part 32…Second diameter part 33...Tapered section 33a... Tapered surface 34... Covering part 40…Fiber housing section 41...First Detention Unit 42...Inner diameter conversion section 43...Second Detention Unit 44a...Inner self A... Direction B1…boundary B2…boundary B3...Boundary B4…boundary C1... Contact point CE…Central axis d1…Diameter d2…Diameter L... Distance between tapered sections R... Bending radius R1…area R2…area S... Split sleeve S1... line segment

Claims

1. A ferrule that includes a fiber housing portion formed in a hollow shape with a circular cross-section and extending in the first direction, The system comprises a plurality of optical fibers housed in the aforementioned fiber housing section, Each of the plurality of optical fibers includes a first diameter portion, a second diameter portion having a larger diameter than the diameter of the first diameter portion, and a tapered portion connecting the first diameter portion and the second diameter portion by a tapered surface having a tapered shape. The fiber housing portion includes a first housing portion and a second housing portion having an inner diameter larger than the inner diameter of the first housing portion. Each of the plurality of optical fibers has a first diameter portion located in the first housing portion. Each of the aforementioned plurality of optical fibers has a second diameter portion located in the second housing portion, The second housing section includes a plurality of regions separated by a plurality of virtual planes perpendicular to the first direction, An optical fiber bundle structure in which the tapered portions of at least two adjacent optical fibers among the plurality of optical fibers are each located in different regions among the plurality of regions.

2. The multiple first diameter portions included in the multiple optical fibers are arranged in the first housing portion at a first pitch. The optical fiber bundle structure according to claim 1, wherein the plurality of second diameter portions included in the plurality of optical fibers are arranged in the second housing portion at a second pitch equal to or greater than the first pitch.

3. The optical fiber bundle structure according to claim 1 or claim 2, wherein the tapered portions of optical fibers that are not adjacent to each other among the plurality of optical fibers overlap when viewed from a direction perpendicular to the first direction.

4. The optical fiber bundle structure according to claim 3, wherein the length of the first housing portion in the first direction is 2 mm or more.

5. The optical fiber bundle structure according to claim 4, wherein, in the first direction, the distance between the tapered portions of adjacent optical fibers is 0.2 mm or more.

6. The optical fiber bundle structure according to claim 5, wherein the plurality of tapered portions included in the plurality of optical fibers are located within the second housing portion.

7. The optical fiber bundle structure according to claim 6, wherein in the first direction, the distance between the tapered portions of adjacent optical fibers is 0.7 mm or less.

8. The aforementioned plurality of optical fibers consist of four optical fibers, The optical fiber bundle structure according to claim 1 or claim 2, wherein the tapered portions of the four optical fibers are each located in different regions among the plurality of regions.

9. The optical fiber bundle structure according to claim 1 or claim 2, wherein the length of the first housing portion in the first direction is 2 mm or more.

10. The optical fiber bundle structure according to claim 1 or claim 2, wherein, in the first direction, the distance between the tapered portions of adjacent optical fibers is 0.2 mm or more.

11. The optical fiber bundle structure according to claim 1 or claim 2, wherein the plurality of tapered portions included in the plurality of optical fibers are located within the second housing portion.

12. The optical fiber bundle structure according to claim 1 or claim 2, wherein in the first direction, the distance between the tapered portions of adjacent optical fibers is 0.7 mm or less.

13. The optical fiber bundle structure according to claim 1 or claim 2, wherein the adjacent optical fibers are configured such that when light with a wavelength of 1.55 μm is transmitted through them, the optical loss is 0.15 dB or less when the optical fibers are wound once in a ring shape with a radius of curvature of 5 mm.

14. The optical fiber bundle structure according to claim 1 or claim 2, wherein the adjacent optical fibers are configured such that when light with a wavelength of 1.625 μm is transmitted through them, the optical loss is 0.45 dB or less when the optical fibers are wound once in a ring shape with a radius of curvature of 5 mm.

15. The optical fiber bundle structure according to claim 1 or claim 2, The multicore fiber comprises a plurality of cores extending in the first direction and a cladding covering the plurality of cores, An optical connection structure in which at least one of the plurality of cores contained in the multicore fiber and at least one core of the plurality of optical fibers are optically coupled.

16. A ferrule including a fiber housing portion formed in a hollow shape with a circular cross-section and extending in a first direction, and including a first housing portion and a second housing portion having an inner diameter larger than the inner diameter of the first housing portion; and a plurality of optical fibers housed in the fiber housing portion, each including a first diameter portion, a second diameter portion having a diameter larger than the diameter of the first diameter portion, and a tapered portion connecting the first diameter portion and the second diameter portion by a tapered surface having a tapered shape; A step of pushing the plurality of optical fibers into the ferrule so that the first diameter portion of the plurality of optical fibers is inserted into the first housing portion, The process includes the step of pulling the multiple optical fibers in the opposite direction to the direction in which they were pushed after the multiple optical fibers have been pushed into the ferrule. The second housing section includes a plurality of regions separated by a plurality of virtual planes perpendicular to the first direction, A method for manufacturing an optical fiber bundle structure, comprising the step of pulling the plurality of optical fibers, wherein, while maintaining the state in which the first diameter portion of each of the plurality of optical fibers is located in the first housing portion, the second diameter portion of each of the plurality of optical fibers is located in the second housing portion, and the tapered portions of at least two adjacent optical fibers among the plurality of optical fibers are located in different regions among the plurality of regions, the plurality of optical fibers are pulled in the direction in which they were pushed in.

Images